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Ch.14 Mendel and the Gene Idea These notes are going to be relatively short because I believe practicing with problems is the best way to cover genetics. Obviously, this is Gregor Mendel.
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Mendel’s discoveries A Blending- Hereditary material- Both parents contribute genetic material. BInheritable factors, genes are passed from generation to generation
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Pea experiments 1. Worked with 7 traits 2. Used purebreeding plants first then crossed them.
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Mendels Pea Crosses
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Law of independent assortment-see Law of independent assortment-see random orientation in ch.16.. ahomologous chromosomes move independently. bEx. Chromosome with A or a will go separate from chromosome with B or b.
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Law of Segregation Homologous pairs segregate during gamete formation(meiosis ) and pair again after fertilization Ex. If a pea is Pp then half the gametes will receive a P and half a p.
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Know the vocabulary Homozygous Heterozygous Phenotype Genotype
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Testcross- Mating an unkown to a homozygous recessive
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Monohybrid Cross- a cross between parents that are heterozygous for one trait.
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Dihybrid Cross
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Incomplete dominance Incomplete dominance leads to a blending of traits, red + white yields pink
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Codominance - is not a blending but a mixing of the traits
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Codominance Codominance - A and B are both dominant to O but not to each other, giving the AB blood type
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Epistasis One gene has an effect on another. C leads to deposition of color while B or b leads to color BBcc would be white even though the genes code for black color.
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Polygenic inheritance Combinations of genes can yield cumulative effects. The more dominant alleles the more color.
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Environmental Effects Sometimes the environment can change the way a gene is expressed, like these hydrangia, and the color based on pH of the soil.
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Pleiotropy One gene can have an effect on other parts of the body. The sickle cell gene which causes problems with blood cells has far reaching affects on the body.
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Pedigree analysis- square is male,circle is female.
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Achondroplasia
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Amniocentesis
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Cystic Fibrosis
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Sickle Cell Anemia
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Tay- sachs
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Huntington’s Corea
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Sample problems Mendel crossed short and tall pea plants(purebred cross) TT x tt = P gen. t t T Tt Tt All offspring are heterozygous T Tt Tt All are tall (Tt)
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Mendel crossed round, yellow pea plants to wrinkled, green pea plants (RRYY x rryy) The only possible gametes are RY from parent 1 and ry from parent 2 so ry ry RY RrYyRrYy All offspring are round RY RrYy RrYy and yellow (RrYy)
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Monohybrid Cross -two heterozygotes mated Tt xTt T t T TT Tt 1TT:2Tt:1tt t Tt tt 3 tall: 1 short
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Dihybrid cross Heterozygotes for 2 traits are crossed RrYy x RrYy You can make the folowing gametes for each parent RY,Ry,rY,ry, this means a four by four box as in the next slide
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Dihybrid Cross
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Dihybrid crosses can also be done like this; R r Y y R RR Rr Y YY Yy r Rr rr y Yy yy Now calculate the chances of RRYY (1/4 x 1/4) RRYy (1/4 x2/4) RrYY (2/4 x 1/4) RRyy (1/4 x 1/4) RrYy ( 2/4 x 2/4) Rryy (2/4 x 1/4) rrYY (1/4 x/1/4) rrYy (1/4 x 2/4) rryy (1/4 x 1/4)
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